We recommend you open a file at West Point during the spring of your junior year. The bulk of the application process takes place in the fall of your senior year. West Point does not have Early Action, but does have a rolling admissions process. It is best to apply early (Aug/Sep) to give yourself time to complete required tests and evaluations and to complete the admissions packet.
You should apply for a nomination at the same time you open a candidate file at West Point, preferrably during the spring of your junior year. Write a letter to your congressional representative and request a nomination. Members of Congress determine their own application deadlines, so apply early. A candidate cannot be offered admission without a nomination.